Methods and systems for marking pixels for image monitoring

ABSTRACT

A method and a computer readable medium containing instructions for devices marking pixel data as being critical symbology pixel data for verification prior to being displayed a pixel on a display device is presented. The method comprises determining by a computing device whether the pixel data is critical symbology pixel data and assigning an intensity threshold level to the pixel data. The threshold is based at least in part on the status of the pixel data as being critical symbology pixel data. Further, the method includes determining whether an intensity of the pixel data is less than or equal to the assigned intensity threshold level and then marking the pixel data as critical symbology pixel data when the intensity of the pixel data is greater than the intensity threshold.

TECHNICAL FIELD

The present invention relates to the field of video processing, and more particularly to a method and system for image monitoring.

BACKGROUND

An operator of a system often relies upon visual indicators to show, among other things, the status of the system. For example, the operator of an aircraft can be provided with indicators such as a visual indicator of the horizon line of the aircraft, a visual indicator of the airspeed of the aircraft, and a visual indicator of the altitude of the aircraft. At one time these visual indicators were provided using analog, mechanical displays. Increasingly, electronic display panels, comprised of a number of individually addressable pixels, are being used to provide visual indicators of system status. Typically, to display the symbology that provides visual indicators, a graphics processing unit is used to generate the symbology, which is then displayed on a display. The proper generation of the symbology is needed to provide the operator an accurate indicator of system status.

Because of the importance of correctly displaying critical symbology, the data sent to the display is typically monitored to determine if the critical symbology was correctly rendered. In a typical prior art system, the display system includes a server that receives information regarding the images to be displayed from a display processor, such as an airborne system, and generates commands to produce images. The commands are received by a graphics processing unit, which uses the commands to generate the image to be displayed by determining the state of each pixel in the image based on the generated commands. The display receives the information regarding each pixel in the display and sets each pixel that comprises the image to the proper state.

In prior art systems, the data produced by the display processor and the data produced by a rendering engine can be monitored or checked. The display commands produced by the display processor from input data are received by a comparator circuit (or processor). The comparator circuit also receives the same input that the display processor uses to generate the display commands. Since in prior art systems the input data from the display commands can be extracted, the comparator circuit compares the data from the display processor with data that the comparator circuit calculated from the input. If there is a match, this part of the verification passes and the display processor is considered to be producing the correct commands from a given input.

In one prior art system, the display processor also inserts a sequence of test commands in the commands sent to the rendering engine. These commands generate test images in an extended area of the display that is not visible to the user. The display output of the rendering engine sent to the extended area of the display is sampled and a cyclic redundancy check (CRC) value is calculated from the sample data. The CRC value is then compared to an expected CRC value to determine if there is a failure in the rendering engine.

While the prior art systems were adequate for monitoring many display systems, an increasing reliance on commercial off the shelf (COTS) display chips has made the task of monitoring display systems more difficult and problematic. One reason is because the architecture of display systems, especially those based on COTS display chips, has undergone changes that render previous monitoring systems inadequate. For example, some COTS rendering engines include integrated circuits that may incorporate functions previously performed in the display processor. This change makes previous methods of monitoring display systems unusable, as it is impractical to extract the commands used to generate pixel data.

Accordingly, it is desired to provide a method and system for image monitoring. Furthermore, the desirable features and characteristics of the present invention will be apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.

BRIEF SUMMARY

In one embodiment, a method for marking pixel data as being critical symbology pixel data for display by a pixel on a display device is provided for. The method comprises determining by a computing device whether the pixel data is critical symbology pixel data and assigning an intensity threshold level to the pixel data, the intensity threshold level based at least in part on a status of the pixel data as critical symbology pixel data. The method further comprises determining whether an intensity value of the pixel data is less than or equal to the assigned intensity threshold level and marking the pixel data as critical symbology pixel data when the intensity value of the pixel data is greater than the assigned intensity threshold level.

In another embodiment, a computer readable storage medium is provided for that contains instructions that when executed mark pixel data as being critical symbology pixel data to be displayed by a pixel on a display device. The instructions comprise determining whether the pixel data is critical symbology pixel data and assign an intensity threshold level to the pixel data. The intensity threshold level is based at least in part on a status of the pixel data as critical symbology pixel data. The instructions further comprise determining whether an intensity value of the pixel data is less than or equal to the assigned intensity threshold level and marking the pixel data as being critical symbology pixel data when the intensity value of the pixel data is greater than the assigned intensity threshold level.

In another embodiment, a computing device is provided for. The computing device determines whether pixel data is critical symbology pixel data and assigns an intensity threshold to the pixel data based at least in part on its status as a critical symbology pixel data. The computing device also determines whether an intensity value of the pixel data is less than or equal to the assigned intensity threshold of the pixel data and mark the pixel data as critical symbology pixel data when the intensity value of the pixel data is greater than the assigned intensity threshold.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and:

FIG. 1 illustrates an exemplary embodiment of a monitored display system;

FIG. 2 illustrates an exemplary embodiment of a graphics processing unit;

FIG. 3 illustrates an exemplary intensity profile used for generating symbologies in accordance with embodiments;

FIG. 4 illustrates an exemplary embodiment of a line to which an intensity profile can be applied in accordance with embodiments;

FIG. 5 is a logic flow diagram for a method of marking pixels using relative pixel intensity data;

FIG. 6 illustrates an exemplary embodiment of a graphics logic device;

FIG. 7 illustrates an exemplary embodiment of an image on a display unit and a bit map stored in memory of the graphics logic device;

FIG. 8 illustrates an exemplary embodiment of a portion of a display showing marked critical symbology;

FIG. 9 is a flowchart of an exemplary method of locating critical symbology in a display and saving to a bit map in accordance with embodiments;

FIG. 10 is an exemplary bit map in accordance with embodiments;

FIG. 11 is a flowchart illustrating an exemplary method for detecting and isolating characters in the bit map in accordance with embodiments;

FIG. 12 is a flowchart illustrating an exemplary method for taking characters saved in the bit map and decreasing them in size to allow for sending to the monitor warning function device in accordance with embodiments; and

FIG. 13 is an exemplary embodiment of a character map.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and is not intended to limit the subject matter of the application and uses thereof. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.

An image monitoring method and system, in one exemplary embodiment, retrieves pixel information associated with critical symbologies such as a horizon line on an aircraft display, an alphanumeric representation of air speed and altitude, and the like, generated by a graphics processing unit. The pixels associated with the critical symbology are marked to allow retrieval by a graphics logic device. The pixels received at the graphics logic device can then be sent to a monitor warning function device where the symbology represented by the captured pixels can be matched to a template or correlated with a template to verify the accuracy of generated pixels.

FIG. 1 illustrates an exemplary embodiment of a monitored display system 100 in accordance with the teachings of the present subject matter. Monitored display system 100 includes a display processor 102 coupled to a graphics processing unit (GPU) 104. The GPU 104 is coupled to a graphics logic device 106 that couples to a display unit 108. A monitor warning function device 110 is coupled to the graphics logic device 106 via the display processor 102. A system bus 101 couples the display processor 102 and the monitor warning function device 110.

Display processor 102 receives data from other systems to generate graphics commands for the GPU 104. The display processor 102 generates data in world coordinates, which are Cartesian coordinates using actual measurement units, as opposed to pixel coordinates, which are used as a coordinate system referenced to the display unit 108. In one embodiment, the input to the display processor 102 can be data such as a commanded change in an airplane's pitch or roll received over the system bus 101. This data can then be used to generate commands for the GPU 104. A myriad of other system data can also be supplied to the display processor 102.

In one exemplary embodiment, the display processor 102 identifies one or more critical symbologies to be checked by the monitored display system 100. Critical symbols can be any graphical symbol, including lines and curves, or alphanumeric characters that can be displayed on the display unit 108. The graphical symbols and alphanumeric characters are considered to be critical symbologies because of the importance of correctly displaying the symbols and characters. The display processor 102 can send data to the GPU 104 indicative of the identity of the critical symbology to be monitored such that the pixels belonging to the critical symbology can be marked. This will be discussed in greater detail below. The critical symbology can be selected from a stored list of critical symbology that can be checked by the monitored display system 100. In one exemplary embodiment, when there are multiple display windows on a display unit 108, one or more critical symbologies per display window can be selected. In one exemplary embodiment, multiple critical symbols in a single window can be detected by marking one critical symbol per the update of the display and then sequencing through each of the critical symbols in subsequent updates to the display.

GPU 104 receives commands from display processor 102 and generates pixel data, typically comprising red, green, and blue color intensity values, an alpha value denoting opacity, and pixel location coordinates denoting location of the pixels with respect to a display unit. In an exemplary embodiment, GPU 104, as illustrated in FIG. 2, comprises a geometry engine 202 coupled to a rendering engine 204. The rendering engine 204 is coupled to a pixel buffer 206. The pixel buffer 206 is coupled to a readout engine 208. A video input 207 is also coupled to the readout engine 208. A non-limiting example of a suitable GPU 104 is the ATI Radeon E4690 manufactured by Advanced Micro Devices of Sunnyvale, Calif.

Geometry engine 202 receives commands from the display processor 102 and performs any necessary rotation, translation or other geometrical and spatial manipulation of the data. The rendering engine 204 receives the output of the geometry engine 202 and performs the calculations necessary to generate pixel data and pixel location coordinates for each pixel in the image to be displayed on the display unit 108. In one exemplary embodiment, pixel data may comprise 8 bits of red value, 8 bits of blue value, 8 bits of green value, and 8 bits of an opacity value. The pixel data for each pixel can be saved to pixel buffer 206. The readout engine 208 can read the pixel data stored in the pixel buffer 206 for presentation to the graphics logic device 106.

In some embodiments the rendering engine 204 may comprise a pixel shader module 205. A pixel shader is a computational kernel function that computes color and other attributes of a pixel. A computational kernel is a software object that takes a given set of input data and returns output data based on the given input. Pixel shaders may range in function from always outputting the same color, to applying a lighting value, to generating shadows, specular highlights, translucency and other visual phenomena. A pixel shader may operate only on a single pixel, without knowledge of a scene's overall geometry. Pixel shaders may be implemented as software, hardware firmware or a combination thereof.

In at least one exemplary embodiment, the GPU 104 “marks” the pixels of the critical symbologies such that they can be retrieved by the graphics logic device 106 for monitoring purposes. The pixels of the critical symbologies are marked by setting the least significant bit of at least one of the color values to a “1” value and all of the least significant bits of that color to “0” for all pixels that are not part of the critical symbology. In other embodiments, the GPU 104 may exaggerate (e.g., increases) the relative intensity difference between pixels of the symbologies and considers those above a certain threshold to be marked pixels based solely on their relative intensity values.

In order to verify that critical symbology has been correctly rendered, it is not necessary to mark all pixels for the symbol. For example, not every pixel in a line needs to be marked in order to retrieve a representation of the line that can be used in the monitoring process. In a typical embodiment, to generate a line, character, or other shape for display on the display unit 108, a texture is applied to the shape using the rendering engine 204. An exemplary intensity profile 302 representing a texture is illustrated in FIG. 3. The intensity profile 302 includes a peak 303 at a center line 305 of the intensity profile 302. The intensity values drop off on either side of the centerline 305. The intensity profile 302 can be applied to a shape, character or line such that the intensity profile represent a peak intensity profile at the center of the symbology with the intensity decreasing according to the intensity profile 302. This particular anti-aliasing scheme is representative of the current embodiment. This invention can also be used with other anti-aliasing mechanisms, such as area coverage, multi-sampling, or with no anti-aliasing mechanism.

FIG. 4 illustrates a line 402 to which the intensity profile 302 has been applied. The line 402 includes a center line 404, which has the highest intensity value of the line 402 according to the intensity profile 302. In the embodiment of FIG. 4, the centerline 404 bisects pixel 406 having the highest intensity. Adjacent to the most intense pixel 406 at centerline 404 are pixels 408 having lesser intense intensity values. The intensity in the line 402 decreases as the distance from the center line 404 increases.

Pixels forming a representation of the critical symbology may be marked using relative intensity derived from the pixel values along or near the center line 404 of line 402. This can be done by exaggerating the intensity difference between critical pixels and other pixels using an appropriately programmed pixel shader module 205 configured to execute a pixel marking method using pixel intensity included in the set of pixel data that is to be rendered on a viewing device. An exemplary embodiment of such a suitable pixel marking method is the method 520 of FIG. 5. The term “pixel data” as used herein means a set of binary code (8-bit or otherwise) providing data to a particular pixel that includes, inter alia, an alpha intensity value and at least one of a red, blue or green intensity level value.

The pixel marking method begins at process 525 where it is determined whether or not a pixel is a critical symbol pixel by methods discussed elsewhere herein. For a pixel identified as a part of a critical symbol, an intensity threshold value 304 (e.g., see, FIG. 3) is assigned to that pixel at process 535. The intensity threshold value may be any desired value between 0 and 1.0. For exemplary purposes, the intensity threshold value 304 for pixel data identified as part of critical symbology will herein be assumed to be 0.8. For a pixel that is not identified as part of a critical symbol, an intensity threshold of 1.0 is assigned to that pixel at process 530.

At process 540, each pixel is rendered and the resulting red, green, blue and alpha intensities are provided to the pixel shader module 205. The alpha (α) intensity is a characteristic of each set of pixel data and has a value between 0 and 1.0. A value of 0 means the pixel has no image coverage or overlay and is transparent. A value of 1 means that the pixel is opaque. It is common in the art to multiply the color intensity by the alpha value to save on computation resources during compositing of an image. The (R,G,B) intensities, at this point, also vary between 0 (i.e., dark) and 1.0 (i.e., fully intensified).

At decision point 545, it is determined if the pixel being processed has am (R,G,B) intensity that is less than, or that is less than or equal to, the threshold assigned to the pixel in either of processes 530 or 535. When a pixel has an (R,G,B) intensity that is less than or equal to its assigned threshold, then the pixel's intensity is scaled down (i.e. multiplied) by a compression factor that is less than 1.0 at process 550.

For exemplary purposes the compression factor herein will be assumed to be 0.75. In some embodiments more practical settings may include an intensity threshold 304 equal to 0.8706 (i.e., 222.0/255.0) and a compression equal 0.86275 (i.e., 220.0/255.0). For pixels of non-critical symbology, their intensity thresholds are equal to 1.0 which is the very highest level and maximum output intensity will be 1.0*0.75=0.75. Thus, non-critical symbology pixels would all be compressed. Similarly, all pixels of a critical symbology with intensities equal to or below 0.8 would also be compressed (e.g., 0.8*0.75=0.6). Note that this results in a discontinuity for pixels included in a critical symbol with marked pixels having a compressed (i.e., reduced) intensity in the range of 0.8 to 1.0 and non-marked pixels having a compressed (i.e., reduced) intensity in the range of 0 to 0.6. Pixels included in non-critical symbols vary in the range of 0 to 0.75 and are thus unmarked.

The compression or scaling process 550 temporarily reduces the intensity values of pixels that were not identified as being part of a critical symbology and also reduces the intensity values of the pixels that were identified as being part of a critical symbology but with intensities below the threshold and thus too low for proper comparison to a template in the monitor warning function device 110, as discussed below.

However, when a pixel has an (R,G,B) intensity that is greater than its assigned threshold, then the pixel's intensity is not modified (e.g., 0.81*1.0=0.81) Thus, in the example, there is a 33% minimum difference between the intensities of the lowest marked pixels (0.81) and the unmarked pixels (0.60). For both marked and unmarked pixel data the method 520 then proceeds to process 555.

At process 555, all marked and unmarked pixels are pre-attenuated. Pre-attenuation means the pixel data (R,G,B) intensity values are reduced further but are kept greater than or equal to zero. Pre-attenuation is performed to prevent intensity creep during alpha blending, described later. Intensity creep is a phenomenon where multiple lines or symbols intercept at a single pixel such that the round-off errors associated with the numerous floating point conversions of the intensities to integer representation can cause a non-critical pixel to exceed its threshold. This phenomenon is eliminated by modifying the alpha blending function to force it to truncate pixel intensities during the floating point conversion. This pre-attenuation is not necessary if the GPU has an option to select between rounding and truncation after alpha blending, but this function appears not to be well known in the art.

As a conventional example, given an alpha of 0.75 and an (R,G,B) intensity level of 254, then alpha*intensity equals 190.5, which is conventionally rounded up to 191. However, if numerous lines utilize that same pixel and each happens to cause a roundup, then the pixel intensity will gradually increase to a final value that could exceed the marked pixel threshold of 0.8 (e.g., with intensity level of 204). This effect increases significantly as the compression factors for pixel data approach the threshold value. To avoid this effect, each pixel intensity value is individually attenuated prior to alpha blending according to embodiments.

The pre-attenuation may be implemented as desired by the system designer and theoretically may take the form of a color attenuation factor. The color attenuation factor equals [−(0.5/255)/alpha] or equivalently [0.0019608/alpha] for embodiments where alpha is represented as an 8-bit value. However, intensity creep may still occur as alpha approaches zero. Hence, in preferred embodiments the pre-attenuation of the intensity from process 550 is determined as the reduced intensity less a color attenuation factor as given by: Color Attenuation=−0.001*(3−α)/α, where

-   -   α is the alpha intensity value of the pixel data, which varies         between 0 and 1.0.         Thus, the color attenuation factor varies linearly between         −0.002/α and −0.003/α, assuming that 8-bit intensity values are         used by the pixel buffer 206. The −0.002 factor is equivalent to         subtracting approximately 0.5 of the reduced (R,G,B) intensity         value (i.e. 0.5/255=0.0019608) determined at process 555. In         equivalent embodiments, other linear or non-linear scaling         functions can be used to address a particular application.

To ensure that the (R,G,B) intensity value is truncated in all situations and never increases, the color attenuation numerator is increased linearly as alpha varies between 1 and 0 such that the color attenuation factor is 50% larger as alpha approaches 0 than it is as alpha approaches 1. As such, the attenuation function always results in truncation. In practical application, it is acceptable to slightly “over truncate” to avoid any possibility of intensity “creep”.

At process 560, each pixel intensity is alpha blended and stored in the pixel buffer 206. Alpha blending is a well known process in the art with several variants. Alpha blending is a convex combination of two colors allowing for transparency effects in computer graphics. In normal alpha blending, the value of α in the color code ranges from 0.0 to 1.0, where 0.0 represents a fully transparent color, and 1.0 represents a fully opaque color. The value of the color C1 having an alpha value of α is overlaid an opaque background of color C0 with an intensity of (1−α), given by: Final Intensity=(1−α)C0+αC1. However, other alpha blending algorithms may also be utilized such as alpha source saturation. For additional information on alpha blending see co-owned U.S. Pat. No. 7,369,139 which is herein incorporated by reference in its entirety.

Thus, after pre-attenuation and normal alpha blending, a final pixel intensity of the pixel data in the pixel buffer 206 is the following: Final Intensity=int(255(α*Modified Intensity+(1−α)*Old Intensity)+0.5), where

-   -   int=integer function (truncate to largest integer<=original         value),     -   New Intensity=desired intensity to be inserted (after         compression)     -   Modified Intensity=New Intensity−Color Attenuation, and     -   Old Intensity=the intensity value currently in the pixel buffer.         Thus, for example, after substitution the Final Intensity after         pre-attenuation is given by:         int(255*(α*(New Intensity−0.0019608/α)+(1−α)*Old Intensity)+0.5)         int(255*α*(New Intensity−0.0019608/α)+255*(1−α)*Old         Intensity)+0.5)         int(255*α*New Intensity−0.5+255*(1−α)*Old Intensity+0.5)         int(255*α*New Intensity+255*(1−α)*Old Intensity)         int(255*(α*New Intensity)+(1−α)*Old Intensity))

All pixels, both marked and unmarked, can be stored in the pixel buffer 206 for retrieval by the readout engine 208 of the GPU 104 for transmission to the graphics logic device 106. patent application Ser. No. 10/851,972, entitled “Texture Based Method And System For The Anti-Aliasing Of Lines and Characters” by Hancock et al. discloses a method for applying intensity profiles to form texture lines, and is hereby incorporated by reference.

At process 565, the pixel buffer is read out and each pixel is communicated to the graphics logic device 106. At decision point 570, the graphics logic device 106 determines if the pixel intensity is less than the pixel's assigned threshold value from processes 535 and 530. If so, the pixel is decompressed in process 580 by multiplying intensity by the reciprocal of the scaling factor (e.g., 1/0.75=1.33) to restore the (R,G,B) intensity value back to an approximation of its original level. If not then the pixel is processed according to the critical (i.e., marked) pixel process 575 discussed further herein below in regard to FIGS. 6-13. The pixel(s) is then output to the display unit 108 at process 585.

Referring again to FIGS. 1 and 2, video input 207 can receive video, such as video from a video camera mounted on an aircraft that shows the status of an aircraft component, and prepare the video for merging with graphical or alphanumeric characters produced by the rendering engine 204.

Graphics logic device 106 receives pixels sent via readout engine 208 and, as pixels are received, detects the marked pixels for storage and presentation to the monitor warning function device 110. Graphics logic device 106, in one embodiment, as illustrated in FIG. 6, comprises an integrity monitoring function 502 coupled to a display function 504. A logic device memory 503 is coupled to the integrity monitoring function 502.

The integrity monitoring function 502 checks each pixel for the marked state and stores all of the marked pixels and/or data regarding the marked pixels in logic device memory 503. The marked pixels can be read out from the logic device memory 503 and transmitted to the display processor 102, which can send the data to the monitor warning function device 110. As discussed above, in some embodiments marked pixels must exceed the intensity threshold based on their processed intensity values, as described in regard to FIG. 5, or have their least significant bits set at a “1” in other embodiments.

Display function 504 performs all processing necessary to prepare the pixels rendered at rendering engine 204 for presentation to the display unit 108. For example, display function 504 can format the pixels such that pixels can be sent over a fiber channel connection between the graphics logic device 106 and the display unit 108.

Logic device memory 503, in one embodiment, can store all data associated with marked pixels such as the location of the marked pixels relative to the display screen, a character map of a detected character, and the like.

Turning back to FIG. 1, display unit 108 receives image data sent from the graphics logic device 106 to produce an image. Display unit 108 can be any pixel based display, such as cathode ray tube displays and LCD displays. Exemplary displays are manufactured by Honeywell, Inc.

Monitor warning function device 110 receives data representative of the pixels of the critical symbology and verifies the critical symbology was accurately generated. In one embodiment, the data representative of the critical symbology can be compared to templates stored at the monitor warning function device 110. The monitor warning function device 110 can receive the same inputs as display processor 102 via the system bus 101 and can independently determine what the critical symbology should be. The independently determined critical symbology can be used to select a proper template, generate a template, or directly used to compare with the data representative of the critical symbology as detected by the graphics logic device 106.

In one exemplary embodiment, a correlation between the critical symbology detected from the pixels generated by the rendering engine 204 and a template of what should be the critical symbology can be calculated to determine if there is a match. A method and system for determining a correlation between critical symbology and a template is disclosed in U.S. patent application Ser. No. 10/868,438, entitled “Image Monitoring Method and System,” which is hereby incorporated by reference.

As discussed previously, the marked pixels and other information regarding the critical symbology is detected at the graphics logic device 106. Data concerning the critical symbology, such as the marked pixels, the location of a window containing the critical symbology as referenced to the display unit 108, a representation of the alphanumeric characters of the critical symbology and the like can be stored to the logic device memory 503. As discussed previously, critical symbology can be geometric symbols, such as a horizontal line on an aircraft display, or alphanumeric characters, such as airspeed of an aircraft. The critical symbology can comprise multiple characters which can be alphanumeric characters or graphical characters. Regular critical symbols 99 should have at least one color intensity (R,B,G) fully saturated (e.g., at a level 255). The same is true for the background color for inverted characters. In one exemplary embodiment, the detection, storage, and sending of graphical critical symbology differs from the detection, storage, and sending of alphanumeric critical symbology.

For graphical critical symbology, in one exemplary embodiment, data representative of all the marked pixels is stored to a memory such as logic device memory 503. For example, in the case of a line, the location on the display (screen location) for every marked pixel in the line is stored to the logic device memory 503. In one exemplary embodiment, the graphics logic device 106 sends pixel locations for a first end point of the line and a second end point of the line, a pixel value for the midpoint of the line, and a pixel value for the part between the first endpoint of the line and the midpoint of the line (the point at one-fourth of the line) and the point between the midpoint of the line and the second endpoint of the line (the point at three-fourths of the line) to the monitor warning function device 110. The data sent by the graphics logic device 106 can be compared to pixel locations of an independently generated graphical critical symbology rendered at the monitor warning function device 110 for verification of the accuracy of the rendering of the critical symbology in the GPU 104. The number of pixels returned can be varied from 1 to as many as desired. One pixel can be used only to detect translation or fixed rotation, while two pixels can be used to detect translation and rotation, and more than two pixels can be used to detect shape. Any other compression technique can be used to reduce the volume of data, such as an endpoint with the slope and length rather than two endpoints. In an alternative embodiment, the critical symbology can be verified in another manner.

In one exemplary embodiment, the critical alphanumeric symbology displayed on the display unit 108 or in a specific window of a display unit 108 is first located. As discussed previously, the pixels of the critical alphanumeric symbology are marked by setting the value of the least significant bit to a value (“0” or “1”) and setting the least significant bit of all other pixels for the display to a different value and/or by allowing the intensities above the threshold to persist and otherwise compressing the intensities to always fall below the threshold. In an exemplary embodiment, the integrity monitoring function 502 checks all pixels for a marked pixel, scanning from left to right on the display unit 108 or in a display window. As the marked pixels are found, they are saved to a buffer. In an exemplary embodiment, the buffer is a 128 by 128 bit map designed to store a maximum of ten alphanumeric characters (arranged, in an exemplary embodiment, as two rows of five locations).

FIG. 7 illustrates an exemplary image 602 of a display unit 108 and a bit map 603 stored in memory of the graphics logic device 106, such as logic device memory 503. Display unit 108 displays an image 602 that indicates a current airspeed 604 of an aircraft. In the example of FIG. 7, the current airspeed 604 is 430 knots and is the critical symbology to be detected. Assuming that the top center portion of the “3” in FIG. 7 is slightly taller than the lead digit “4”, when the integrity monitoring function 502 checks pixels from left to right and from top to bottom of the display, the top center of the “3” is the first part of the critical symbology detected. At this point, the integrity monitoring function 502 knows only the location of the first marked pixel. What is not known is if the first marked pixel is a character at the beginning of the alphanumeric string. In this case, the first marked pixel detected is not the beginning of the character string. In order to ensure that all detected characters are placed in the bit map 603 without prior knowledge of how many characters could be to the left of the first detected character, the placement of the detected pixels in the bit map 603 is divided between placing detected pixels in a right hand side 607 of the bit map 603 (which can be thought of as negative column positions) and a left hand side 605 of the bit map 603 (which can be thought of as positive column positions).

In one embodiment, the first detected pixel is placed at row 0, column 0 of the bit map. Then, all pixel values in columns to the right of the first detected pixel will correspond to a pixel in the left hand side 605 of the bit map 603. The pixels in any columns that are to the left of the first detected pixel will be mapped to the right hand side 607 of the bit map 603. As seen in the bit map 603 of FIG. 7, the airspeed of 430 is stored as 304. Since the first marked pixel is the center of the “3”, part of the “3” and “0” are saved to the left hand side 605 of the bit map 603 and the character “4” and the rest of the “3” are saved to the right hand side 607 of the bit map 603. Thus, in the bit map 603, the actual first character in the string of critical alphanumeric symbology is not the first character in the bit map 603 and is not a full character, but instead is the character with the greatest negative distance from the position of the first detected character, where negative distance is distance to the left of the starting position.

Once all of the marked pixels are detected and the bit map 603 has been populated, each individual character can be extracted from the bit map 603. Optionally, the characters can be compressed before sending to the monitor warning function device 110 to determine if the detected characters were correctly generated at the correct location.

An exemplary embodiment of the detection of critical symbology and the use of the bit map 603 is shown in FIGS. 8-10. FIG. 8 illustrates a portion of the display that includes the critical symbology, which, in this exemplary embodiment, comprises the number “43” where the “4” is underlined. FIG. 9 is a flowchart of an exemplary embodiment for locating critical symbology in a display or a window of a display and populating the bit map 603 with the detected critical symbology, and FIG. 10 is an exemplary bit map produced by the monitor showing the critical symbology.

Turning to the flowchart of FIG. 9, in step 802 a display detection area is initialized. The display detection area is an area of the display that, if a marked pixel is detected within, a corresponding location in the bit map will be set. The display detection area sets forth, in one exemplary embodiment, a range of columns. The area can be set by two values setting an X_(LOW) and X_(HIGH) value as: X _(LOW)=LastX−C X _(HIGH)=FirstX+C Where FirstX and LastX are values which can be adjusted to adjust the X_(LOW) and X_(HIGH) and C is based on the size of the bit map. The exemplary bit map of FIG. 10 is a 16×16 bit map and C will be set to the width of the bit map −1 or 15 in this case. FirstX and LastX are set using display coordinates. Initially, the FirstX and LastX can both be set to 0 producing X_(LOW)=0 (since there are no negative screen coordinate values the default is 0) and X_(HIGH)=15.

In step 804, the scanning process starts at the pixel at (0, 0) of the display. In step 806, it is determined if the pixel is a marked pixel. If the pixel is not a marked pixel, in step 808 it is determined if the pixel is within the display detection area. If the pixel is not a marked pixel, but is within the display detection area, in step 810, a 0 is stored at a pixel in the bit map. If step 810 occurs before a marked pixel is found, in step 810 a 0 is always stored at position (0,0) of the bit map 603 (the location on the bit map 603 corresponding to the first row and first column).

After a 0 is stored in the bit map 603, it is determined if the pixel just checked was the last pixel in a row in step 812. If it is not the last pixel, in step 816 the process advances to the next pixel of the row.

If the pixel just checked is the last pixel in the row, the process advances to the first pixel of the next row, in step 814 and the process continues in step 806.

In step 808, if it is determined that the pixel just checked is not within the display detection area, the process continues at step 812 where it is determined if the pixel is the last pixel in the row. Then, either the next pixel in the row is checked via steps 816 and 806 or the first pixel in a new row is checked at steps 814 and 806.

Turning back to step 806, if it is determined that the pixel checked is a marked pixel, then, in step 818 it is determined if the marked pixel that was just located is the first marked pixel located.

If the pixel is the first located marked pixel, then, in step 820, a “1” is stored at location (0, 0) of the bit map 603. Referring to FIG. 8, the first marked pixel that will be found is the top center of the “3”, which is at screen position (X_(1A), Y1A).

In addition to setting location (0, 0) of the bit map 603 of FIG. 10 to “1”, in step 826, when the first pixel is detected, FirstX and LastX are both set to the horizontal screen coordinate of the first detected pixel, which in this case is X_(1A). Therefore, X_(LOW)=X_(1A)−15 and X_(HIGH)=X_(1A)+15 in the exemplary embodiment of FIG. 8.

Also, a StartX variable is set to the horizontal screen position of the first detected pixel (X_(1A) in this example) and a TopY variable is set to the vertical screen position of the first detected pixel (Y_(1A) in this example). StartX and TopY are used to set the position of other locations in the bit map 603.

In step 818, if the marked pixel detected is not the first marked pixel, it is determined, in step 822, if the found marked pixel is within the display detection area. In FIG. 8, the next detected pixel will be the upper left part of the “4”, which is located at the screen coordinate of (X₁, Y1). In this example X₁ is clearly within 15 pixels of X_(1A) so the marked pixel is within the display detection area. Had the detected marked pixel not been within the display detection area, the process continues at step 812, as discussed previously.

In step 824, a “1” is stored in the bit map corresponding to the marked pixel. The location in the bit map where the “1” is stored is (X_(CURRENT)−StartX, Y_(CURRENT)−TopY) where X_(CURRENT), Y_(CURRENT) are the display screen coordinates of the current found marked pixel and, as discussed before StartX and TopY are the screen coordinates of the first detected pixel.

In FIG. 8, it can be seen that X₁ is nine pixels to the left of X_(1A) and Y₁ is one pixel below X_(1A). Thus, (X−StartX, Y−TopY) is (−9, 1). Since negative numbers are not used in the bit map, the negative number indicates that to determine the columns to place the “1” in, the columns are counted to the left, wrapping around from the first column where the first detected pixel is located, to the last column and then to the left as needed. For the example above, nine pixels from the first detected pixel, the horizontal location of the pixel is at column 7 (0111 in binary) and the vertical location is at row 1 (one row down from the vertical location (row 0) of the first detected pixel).

After the pixel is stored in the bit map, in step 826, the display detection area is updated. If the horizontal pixel location value is less than FirstX and within LastX−C (where, in the exemplary embodiment of FIG. 10, C is 15). The value of FirstX is replaced by the horizontal pixel location value of the current marked pixel. If the horizontal pixel location value of the current marked pixel is greater than LastX and within FirstX+C (where C is 15 in the exemplary embodiment) then the value of LastX is set to the horizontal pixel location value of the current marked pixel. Since the pixels are scanned sequentially from left to right, FirstX will be updated first, which reduces the X_(HIGH). When LastX is updated, X_(LOW) will increase.

After step 826, the process continues at step 812 as discussed before. The process of scanning for marked pixels will continue until all pixels of a display area are scanned. The critical symbology of FIG. 8 will produce the bit map of FIG. 10.

One way to indicate a character is on the left hand side of the bit map 603 versus the right hand side, is to use a numerical column address that includes a bit indicating if the column is part of the right hand side of the bit map 603. For example, in FIG. 10, the bit map 603 is a 16 by 16 bit map. Thus, each column is addressed using a four bit binary number from 0000(0) to 1111(15). For columns that include the first detected pixel and for every pixel for each character detected to the right of that pixel, the address bit value can have a one (“1”) appended to the front of the address bit. The columns storing pixels detected to the left of the first pixel can have a “0” appended to the front of the address bit (most significant bit). Thus, in FIG. 10, the first column address bit will be 10000 (column 0) while the number four starts at column 00111 (column 7). In one embodiment, by using the full five bits as the column value, the difference between the starting column for each character can be used to determine the original spacing of the character on the display. For example, the “3” starts at column 10000 or 16 and the “4” starts at column 00111 or 7. The difference is 9 columns which is the original column spacing in the display.

FIG. 11 is a flowchart illustrating an exemplary method for detecting and isolating characters in the bit map 603. In a first step, step 1002, the bit map 603 is searched to find marked pixels. In one embodiment, the pixels are searched from right to left, starting with the largest column from the left hand side of the bit map 603. As discussed previously, the columns on the left hand side can have a leading “1” as the most significant digit. Column 0 (0000) thus becomes, in this embodiment is 16 (10000). So, for FIG. 10 pixels will be scanned from right to left starting at column 22 (10110). Each pixel in the bit map 603 is examined to determine if the pixel is marked.

This continues in step 1004, for each column from right to left until no marked pixels are found in two consecutive columns. Then, in step 1006, the starting column with marked pixels, the starting row with marked pixels, the last row with marked pixels, and the last column with marked pixels are saved as the bounding box of the characters.

In step 1008, it is determined if all columns in the bit map 603 have been checked. If not all of the bit map 603 columns have been checked, then the process continues in step 1002. If all of the columns of the bit map have been checked, then in step 1010, for each character found, each row of the columns of the character is examined for marked pixels until either the bottom row of the character is reached or two consecutive rows are found that have no marked pixels.

If two consecutive rows without marked pixels are found, the left most column that includes a marked pixel, the right most column that includes a marked pixel, the top row having a marked pixel, and the bottom row having a marked pixel are stored as determining a new character bounding box in step 1012. Then, in step 1016, it is determined if all of the rows of that character have been examined. If not all of the rows for the selected characters have been examined, then the process continues in step 1010.

If all of the rows and columns of the character have been checked, in step 1018 it is determined if every character found has been examined. If every character has been examined, the process ends. If there are more characters to examine, the process continues at step 1010.

If, in step 1010, each row and column of the character is examined and the bottom row of the character is reached without finding two consecutive rows of unmarked pixels, the character's right column, left column, top row and bottom row are saved as the original character in step 1014. Then, in step 1018, it is determined if all characters have been examined. If all the characters have been examined, the process ends. If not, the process continues at step 1010. This method for locating individual characters works well when the characters are aligned into columns; however there are multiple other methods for locating the individual characters. For example a third sequence of steps similar to steps 1010-1018 could be added to the above method following a “Yes” to step 1018 that examines by columns and rows the characters saved in steps 1010-1018. By adding the third sequence of steps the method of locating individual characters will work well when the characters are not aligned into rows or columns, although it will be slower.

As an example, and with reference to FIG. 10, the bit map 603 is examined for marked pixels starting with any columns belonging to the left hand side of the bit map 603. In the example of FIG. 10, the column addresses to the left hand side begin with a “1”. So, for FIG. 10, the first pixel found is the right pixel of the “3” at row 2, column 18. Then, moving from right to left, and wrapping around to the last column of the bit map to the first column, this is repeated for all columns and rows until there are at least two consecutive columns that have no marked bits. In this example, the “3” ends at column 14, so after column 13 and 12 are examined, the process stops. Then the starting column, column 18 (column 10010, using the most significant bit of “1” to represent the right hand side of the bit map 603), the ending column, column 14, the starting row, row 0, and the ending row, row 12, are stored as the location of the first character, the “3”.

For the “4” and the underscore in the bit map 603 of FIG. 10, after step 1006, the starting column is column 11, the ending column is column 7, the first row is row 1, and the last row is row 15, since the underscore is included with the “4”.

This represents steps 1002-1006. After these steps, for the first character, the “3”, each row of each character is checked for marked pixels until the bottom row of the original column is reached or there are two consecutive rows without a marked bit, which is step 1010. In the example of FIG. 10, for the “3”, the bottom of the originally located character is reached. Thus, the coordinates for the character are the same as before and are resaved in step 1014.

For the “4” and underscore, in step 1010, after the bottom of the “4” is reached there are two blank rows. Thus, a new character is saved of left=column 7, right=column 11, top=row 1, and bottom=row 12. This is saved in step 1012. In step 1016, it is determined if all the rows of the character detected in steps 1002-1008 have been checked. In FIG. 10, there is one more row to check, which is row 15. In row 15, the underscore is then checked in step 1010. In step 1014, the coordinates can be saved, which is row 15, columns 7-11.

In one embodiment, the coordinate value of the top, right bit map location, a delta x value representing the width of the bounding box of the characters, and a delta y value representing the height of the bounding box of the characters can be saved and later sent as the location of the character.

FIG. 12 is a flowchart illustrating a method for taking characters saved in the bit map 603 and decreasing them in size to allow for sending to the monitor warning function device 110. In one exemplary embodiment, all characters in the bit map 603 are rewritten into an 8 by 8 character map. Other sizes of the character map can also be used and the character map does not have to be square (for example 7×9 also fits in 64-bits). This both decreases the resources needed to send the data and standardizes the size of the alphanumerical characters for conversion and correlation to template characters, or other character comparison structures.

In a first step, step 1102, horizontal and vertical compression ratios are calculated based on the following equations:

${{Vertical}\mspace{14mu}{Compression}\mspace{14mu}{Ratio}} = \frac{{Number}\mspace{14mu}{of}\mspace{14mu}{pixels}\mspace{14mu}{in}\mspace{14mu}{the}\mspace{14mu}{{character}'}s\mspace{14mu}{length}}{{Vertical}\mspace{14mu}{size}\mspace{14mu}{of}\mspace{14mu}{character}\mspace{14mu}{map}}$ ${{Horizontal}\mspace{14mu}{Compression}\mspace{14mu}{Ratio}} = \frac{{Number}\mspace{14mu}{of}\mspace{14mu}{pixels}\mspace{14mu}{in}\mspace{14mu}{the}\mspace{14mu}{{character}'}\; s\mspace{14mu}{width}}{{Horizontal}\mspace{14mu}{size}\mspace{14mu}{of}\mspace{14mu}{character}\mspace{14mu}{map}}$

The vertical size of the character map in this example is 8 pixels, the equation is:

${{Vertical}\mspace{14mu}{Compression}\mspace{14mu}{Ratio}} = \frac{{Number}\mspace{14mu}{of}\mspace{14mu}{pixels}\mspace{14mu}{in}\mspace{14mu}{the}\mspace{14mu}{{character}'}s\mspace{14mu}{length}}{8\mspace{14mu}{pixels}}$ The horizontal compression is, therefore:

${{Horizontal}\mspace{14mu}{Compression}\mspace{14mu}{Ratio}} = \frac{{Number}\mspace{14mu}{of}\mspace{14mu}{pixels}\mspace{14mu}{in}\mspace{14mu}{the}\mspace{14mu}{{character}'}\; s\mspace{14mu}{width}}{8\mspace{14mu}{pixels}}$ For all compression ratios, if the ratio is below 1, the compression ratio is set at 1.

Next, in step 1104, it is determined how many compressed rows and/or columns are needed along with how many non-compressed rows and columns are required to map from the bit map to the 8 by 8 character map. For example, if the compression ratio is two to one in the vertical direction, a character 16 pixels tall would need to be compressed to 8 pixels. This requires every two rows in the original bit map 603 to be compressed to one row in the character map.

In step 1106, for each compression row or column, all of the bit values for each bit comprising the compressed rows or columns are read to determine the bit value for each pixel in the character rows and/or columns. In step 1108, for non-compressed rows and columns, the bit values transfer from the bit map 603 to the character map.

As an example of the method in FIG. 11, consider the character “4” in FIG. 10. The character is five pixels wide (the character extends across five columns) and is twelve pixels long (the character extends down twelve rows). Therefore, the compression ratios can be calculated:

${{Vertical}\mspace{14mu}{Compression}\mspace{14mu}{Ratio}} = {\frac{12\mspace{14mu}{pixels}}{8\mspace{14mu}{pixels}} = 1.5}$ ${{Horizontal}\mspace{14mu}{Compression}\mspace{14mu}{Ratio}} = {\frac{5\mspace{14mu}{pixels}}{8\mspace{14mu}{pixels}} = 0.625}$ Since any compression ratio less than 1 is set at 1, the horizontal compression ratio is set at 1, or no compression.

In the vertical direction the compression ration is 1.5. Thus, if two rows are compressed for every one row that is not compressed, the twelve pixels tall “4” can be compressed to eight pixels tall. Thus, the first two rows of the character (row 1 and row 2) are compressed to form a first row 1202 of an 8×8 character map 1201 as illustrated in FIG. 13. In this case, the result is a marked pixel in the first row, first column and the first row, fourth column.

The next row of the character in the bit map 603, row 3, is not compressed and is used as a second row 1204 of the 8×8 character map 1201. The fourth and fifth row of the character are compressed by bringing the pixels of the two rows together to form the third row 1206 of the 8×8 character map 1201. Then, the sixth row of the “4” character in the bit map 603 is used as a fourth row 1208 of the 8×8 character map 1201. This process continues for rows 1210-1216 until the 8×8 character map 1201 is filled.

After all of the characters of the critical symbology are detected, isolated and mapped to a character map, data concerning the detected characters can be sent to the monitor warning function device 110 via, in one exemplary embodiment, the display processor 102. This data can include the bit pattern of each character map for each character, as well as pixel location values to determine the original location of the pixels on the display screen. This information can then be used for comparison purposes with character templates, characters generated by the monitor warning function device 110 or other comparison structures. Multiple compression algorithms can be employed beyond the one presented in this embodiment including no-compression or character pattern matching with correlation to just report the character code.

The above flowchart discusses the marking, detection and processing of critical symbology assuming the alphanumeric characters are regular (bright) characters on a background (such as a red character on a white background). For example, the critical symbology for a line of alphanumeric characters may be bright characters on any background (such as a black background). In this case, the bright areas of the critical symbology can be pass through uncompressed (i.e., marked pixels) and all the background pixels will be compressed. However, certain characters shown in a white or other bright background are known as reverse characters. In reverse characters, the character is not formed by pixels but instead is formed by pixels outlining the character. For example, a black “H” on a white background would appear as an area of white pixels with a number of dark pixels forming the “H” character. The difficulty in this embodiment is that since the center pixels of the character can be black, they are necessarily less than the threshold. In this case, the reverse profile of FIG. 3 is cut into the bright background, resulting in the darkest pixels at the centerline 404 of the line 402.

Therefore, a slightly different approach is required to handle reverse characters. If critical symbology is to be displayed as a reverse character, when the rendering engine 204 is rendering pixels, instead of marking the pixels of the critical symbology, the pixels surrounding the critical symbology are marked as discussed previously. Then, when the pixels are being processed in the graphics logic device 106, any character pixel surrounded by an area of marked pixels is detected and a corresponding bit in the bit map is set to represent that bit. In one exemplary embodiment, the intensity value of the pixel must be below a threshold value as explained in conjunction with FIG. 3 and FIG. 4.

Additionally, in an exemplary embodiment, a video stream may display on a display unit 108 or in one display window of the display unit 108. As discussed previously, the video can be video from a video camera mounted on the airplane and showing a component of the airplane such as the position of the landing gear. Critical symbology may also be merged with the video after the rendering of the pixels by rendering engine 204. When this occurs, the video pixels can have intensity levels above the threshold since the pixels of the video were not processed by the rendering engine 204. Thus, if the graphics logic device 106 only attempts to locate marked bits, the merged video stream can make the detection of marked bits of critical symbology impossible.

To alleviate this problem, the video intensities are unconditionally compressed such that they are always less than the threshold. Recall that the present invention marks the center pixels of the critical symbology, which has the highest intensity value. By holding the intensity value of the video stream below the intensity value of the marked pixels, the integrity monitoring function 502 of the graphics logic device 106 will locate the marked pixels of the critical symbology. Marking only the center most pixels of a line makes the detection more accurate and avoids excessive character bits which would make compression problems since a great many pixels will be sent.

Those of skill in the art will appreciate that the various illustrative logical blocks, modules, circuits, engines and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. Some of the embodiments and implementations are described above in terms of functional and/or logical block components and various processing steps. However, it should be appreciated that such block components may be realized by any number of hardware, software, and/or firmware components configured to perform the specified functions. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention. For example, an embodiment of a system or a component may employ various integrated circuit components, e.g., memory elements, digital signal processing elements, logic elements, look-up tables, or the like, which may carry out a variety of functions under the control of one or more microprocessors or other control devices. In addition, those skilled in the art will appreciate that embodiments described herein are merely exemplary implementations.

The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. The word “exemplary” is used exclusively herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.

The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in a computer readable storage medium. A computer readable storage medium may include any type of memory device. Non-limiting examples of memory devices include RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

In this document, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Numerical ordinals such as “first,” “second,” “third,” etc. simply denote different singles of a plurality and do not imply any order or sequence unless specifically defined by the claim language. The sequence of the text in any of the claims does not imply that process steps must be performed in a temporal or logical order according to such sequence unless it is specifically defined by the language of the claim. The process steps may be interchanged in any order without departing from the scope of the invention as long as such an interchange does not contradict the claim language and is not logically nonsensical.

Furthermore, depending on the context, words such as “connect” or “coupled to” used in describing a relationship between different elements do not imply that a direct physical connection must be made between these elements. For example, two elements may be connected to each other physically, electronically, logically, or in any other manner, through one or more additional elements.

While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims. 

The invention claimed is:
 1. A method for marking pixel data as being critical symbology pixel data for display by a pixel on a display device, the method comprising: determining by a computing device whether the pixel data is critical symbology pixel data; assigning an intensity threshold level to the pixel data, wherein assigning the intensity threshold level comprises assigning a first intensity threshold level to the critical symbology pixel data and a second intensity threshold level to non-critical symbology pixel data, the second intensity threshold level being greater than the first intensity threshold level; determining whether an intensity value of the pixel data is less than or equal to the assigned intensity threshold level; reducing the intensity value of the pixel data for critical symbology pixel data and for the non-critical symbology pixel data by a common compression factor when the intensity value of the pixel data is less than or equal to the respective assigned intensity threshold level, and maintaining the intensity value of the pixel data for critical symbology pixel data and for the non-critical symbology pixel data when the intensity value of the pixel data is greater than the respective assigned intensity threshold level.
 2. The method of claim 1, wherein the second intensity threshold level is 1.0.
 3. The method of claim 1, further comprising pre-attenuating the reduced intensity value of the pixel data resulting in pre-attenuated reduced intensity value of the pixel data.
 4. The method of claim 3, further comprising alpha blending the pre-attenuated reduced intensity value of the pixel data.
 5. The method of claim 3, wherein a degree of pre-attenuation is calculated by reduced intensity−0.001*(3−α)/α, where a is in a range of 0 to
 1. 6. The method of claim 1, further comprising restoring the intensity value by a factor equal to a reciprocal of the compression factor and rendering the pixel data on the display device.
 7. A non-transitory computer readable storage medium containing instructions that when executed mark pixel data as being critical symbology pixel data to be displayed by a pixel on a display device, the instructions comprise: determine whether the pixel data is critical symbology pixel data; assign an intensity threshold level to the pixel data, wherein assigning the intensity threshold level comprises assigning a first intensity threshold level to the critical symbology pixel data and a second intensity threshold level to non-critical symbology pixel data, the second intensity threshold level being greater than the first intensity threshold level; determine whether an intensity value of the pixel data is less than or equal to the assigned intensity threshold level; reducing the intensity value of the pixel data for critical symbology pixel data and for the non-critical symbology pixel data by a common compression factor when the intensity value of the pixel data is less than or equal to the respective assigned intensity threshold level, and maintaining the intensity value of the pixel data for critical symbology pixel data and for the non-critical symbology pixel data when the intensity value of the pixel data is greater than the respective assigned intensity threshold level, and.
 8. The non-transitory computer readable storage medium of claim 7, wherein the second intensity threshold level is 1.0.
 9. The non-transitory computer readable storage medium of claim 7, wherein the instructions further comprise pre-attenuate the reduced intensity value of the pixel data resulting in pre-attenuated reduced pixel intensity data.
 10. The non-transitory computer readable storage medium of claim 9, wherein the instructions further comprise alpha blending the pre-attenuated reduced pixel intensity data.
 11. The non-transitory computer readable storage medium of claim 10, wherein the instructions further comprise restore the intensity value by a factor equal to a reciprocal of the compression factor for display on the display device.
 12. The non-transitory computer readable storage medium of claim 9, wherein the pre-attenuated reduced intensity value is calculated by reduced intensity−0.001*(3−α)/α.
 13. A computing device configured to: determine whether pixel data is critical symbology pixel data; assign an intensity threshold to the pixel data, wherein assigning the intensity threshold level comprises assigning a first intensity threshold level to the critical symbology pixel data and a second intensity threshold level to non-critical symbology pixel data, the second intensity threshold level being greater than the first intensity threshold level; determine whether an intensity value of the pixel data is less than or equal to the assigned intensity threshold of the pixel data; reducing the intensity value of the pixel data for critical symbology pixel data and for the non-critical symbology pixel data by a common compression factor when the intensity value of the pixel data is less than or equal to the respective assigned intensity threshold level, and maintaining the intensity value of the pixel data for critical symbology pixel data and for the non-critical symbology pixel data when the intensity value of the pixel data is greater than the respective assigned intensity threshold level.
 14. The computing device of claim 13, wherein the second intensity threshold level is 1.0. 